Technology advancements in the information recording field is remarkable. And research and development on high-density recording/regeneration and high-speed access for optical memory using light, such as a magneto-optical disk memory, are aggressively on-going. Research and development to enhance such characteristics of an optical disk memory are progressing, and in Japanese Patent Application Laid-Open No. H6-202820, for example, a concurrent ROM (Read Only Memory)—RAM (Random Access Memory) optical disk (hereafter called optical information recording medium), where simultaneous regeneration of ROM and RAM is possible, is disclosed.
Such an optical information recording medium, where the simultaneous regeneration of ROM and RAM is possible, can provide a storage capacity that is double that of an ordinary optical disk memory, and simultaneous regeneration of ROM-RAM, which is impossible for a magnetic disk, is possible.
In the above mentioned prior art, for example, an optical information recording medium where phase pits are formed in spirals or concentrically on an optically transparent substrate, and a magneto-optical recording film is formed thereon, are used. And lights are condensed almost up to the diffraction limit from the optical pickup, and are irradiated onto the optical information recording medium. While the light intensity of the return lights from the optical information recording medium which are modulated by the phase pits, are regenerated as ROM signals, and the differential amplitude of the polarization direction components after modulating the return lights by the magneto-optical recording film are regenerated as RAM signals.
Also a magnetic head, for applying a magnetic field onto the optical information recording medium, is installed in the optical pickup, and RAM signals are recorded onto the magneto-optical recording film by changing at least one of the condensed light and the magnetic field from the optical pickup.
In such an optical information recording medium having ROM information and RAM information on a same recording face, many improvements exist to simultaneously regenerate the ROM information on the phase pits PP and RAM information on the magneto-optical recording OMM.
As an obstacle to stably regenerate the RAM information along with the ROM information, the light intensity modulation generated by reading the ROM information becomes a cause of noise when regenerating the RAM information. For this, the present applicant proposed in U.S. Pat. No. 7,154,836 that the light intensity modulation signals, which accompany the reading of ROM information, are negative-fed back to the laser for read driving.
By this method, the light intensity modulation noise can be decreased and the leak of the phase pit signals into the magneto-optical signals can be decreased. However the laser light emitting element heats up when a drive current is supplied, and the light emission power changes depending on the temperature, even if the drive current value to be supplied is the same. Therefore when the phase pit signals are suppressed by negative-feed backing the light modulation intensity signals to the laser light emitting element according to the above proposal, the suppression gain changes depending on the temperature change, which changes the phase bit crosstalk amount. As a result, the quality of the magneto-optical signals deteriorates, and this proposal alone is not sufficient in terms of the noise reduction effect.